Composite electroplate



United States Patent 3,047,939 COMPUSHTE ELEtJ'lRUPLATE Henry Brown, Huntington Woods, Mich, assignor to The Udylite Research Corporation, Detroit, Mich, a corporation of Michigan No Drawing. Filed Feb. 24, 1959, Ser. No. 794,794 16 Claims. (1. 29-1835) This application is a -continuation-in-part of my copending application, Serial No. 448,365, filed August 6, 1954, now Patent No. 2,900,707, issued August 25,1959, and entitled Metallic Protective Coating.

This invention relates to improvements in the plated sequence of the type of chromium-nickel-chromium plate described in US. Patent 2,871,550, issued February 3, 1959, which gives extraordinary outdoor corrosion protection to commercial metals susceptible to atmospheric corrosion including ferrous metals, zinc die-cast, aluminum, brasses and'magnesium.

The improvements which have been found consist in the use of cobalt with the nickel plate which is sandwiched between the two chromium plates. The cobalt not only adds greatly to the ductility of bright nickel plate used between the two chromium plates, but also increases to a certain and favorable extent the degree of lateral corrosion of the plate between the two chromium plates which is very desirable instead of corrosion penetration downward into the basis metals.

That is, while the sequence of chromium-nickel-chromium plate as described in Us. Patent 2,871,550 gives extraordinary outdoor corrosion protection to the aforementioned commercial basis metals, it has a draw-back that when this laminated plate contains bright nickel plate in between the two chromium plates and the laminated plate is mildly distorted (e.g. a 20 bend), the plate may crack. This is not important for many applications as on zinc die-cast handles or other articles which are not distorted in use, but it is important for many articles of steel, zinc die-cast, aluminum, and brasses which are flexed in normal usage. In the latter cases not only an underneath chromium layer of about 0.03 to 0.06 mil should be because of the intrinsic brittleness of most chromium plates, but the nickel between the two chromium plates should be as ductile as possible and free from serious hydrogen embrittlement from the cathodic gassing during the application of the final chromium plate. In the cases where the chromium-nickel-chromium plate is desired as bright as possible without buffing or polishing of the nickel between the two chromium plates the use of cobalt as described below with the nickel plate in between the two chromium plates makes possible improved ductility of the laminated plate as well as an improvement in corrosion protection when the underneath chromium is only about 0.01 mil thick.

For example, if a low pH cobalt strike, Example I, or a cobalt-nickel alloy strike, Example II, is used directly on the underneath chromium plate and this strike is overlaid with nickel, then because the cobalt and cobalt-nickel alloys are more readily attacked than nickel itself anodically in the corrosion cell, lateral corrosion is more favored even when the underneath chromium is only 0.01 mil thick than when nickel directly overlies a chromium plate of only 0.01 mil thickness. However, even with the cobalt strike it is better to use an underneath chromium layer of about 0.03 to 0.06 mil thick for best outdoor corrosion protection. Furthermore, the use of a bright cobalt-nickel alloy plate, Example IV, either on top of a nickel strike or a cobalt strike or a nickel-cobalt strike between the two chromium plates makes possible a much more ductile laminate than is obtained when the bright nickel plate has no cobalt present. However, to significantly ductilize the 3,047,939. Patented Aug. 7., 1962 "ice bright nickel plate a minimum of about 10% cobalt to a maaimum of about 50% cobalt should be present in the bright nickel plate. The composition of such very ductile bright nickel-cobalt plating baths are shown in Example IV, which gives bright ductile plate even after chromium plating. The percentage of cobalt in this bright plate is about 40%, and this is within the preferred percentage of about 10% to 50% cobalt. Thus, with the use of cobalt or cobalt-nickel strike plates on the underneath chromium plate, of up to about 0.1 mil thickness followed by at least 0.1 mil thick to 2 mils thick nickel plate, or by the use of the cobalt strike, or the cobalt-nickel strike or the nickel strike, Example III, of up to 0.1 mil thickness followed by at least 0.1 mil to about 2 mils thickness of a bright cobalt-nickel plate containing at least 50% nickel, it is possible to obtain improved ductility for the laminate plate as well as improved corrosion protection especially in recessed articles where the underlying chromium plate may be as low as 0.01 mil chromium.

in plating zinc die-cast articles with the laminate of this invention, it is preferred that the zinc castings be given a copper o-r brass plate before the first or lower chromium plate, the underneath chromium, is applied. The lower chromium plate is preferred to be deposited from the crack-free type of high temperature, F. to about F. baths, high ratio type of baths that tend to give a cloudy crack-free plate.

In plating steel, it is preferred to plate the steel first with chromium or if the steel needs to be preliminarily polished because, for example, of an orange-peel surface caused by drawing or forming operations as with automobile steel bumpers or bumper guards, then it is preferred to zinc plate the steel instead of polishing it, then bufling the Zinc to a high luster and then copper plating the zinc before the first chromium is applied. In this case the zinc layer preferably has a thickness of about 0.1 to 2 mils thick before the copper is applied. The copper layer is preferably about 0.1 to about 2 mils thick before the first chromium is applied.

However, the use of copper or copper alloys or nickel underneath the lower chromium is mainly for the purpose of covering over basis metal defects such as oxide and other insulating inclusions, or to obtain increased ductility for the total plate, and therefore very ductile copper or nickel is preferably used underneath the lower chromium plate. In the case of steel articles that are easily polished to a good finish, for example, automobile hub-caps, it is in general preferred to first chromium plate the steel directly with the crack-free type of chromium plate.

In general, the lower chromium plate should have a thickness of at least 0.01 mil and preferably at least about 0.03 mil to a maximum of 0.2 mil. The total thickness of the cobalt containing nickel including the cobalt or cobaltnickel strike which is directly on the underlying chromium followed by nickel or nickel-cobalt alloy, or of a nickel strike directly on the chromium plate followed by a nickel-cobalt plate, should be not less than about 0.2 mil or greater than 2 mils. The final chromium should have a thickness in the range of about 0.005 to about 0.1 mil, and preferably 0.03 to 0.06 mil.

It is to be understood that when nickel plate, cobalt plate or nickel-cobalt plates are referred to, the presence of small percentages of iron or zinc in the bath nevertheless produces plate which is still essentially a nickelcobalt plate. Such impurities may enter the baths, for example, the low pH nickel strikes or cobalt strikes or cobalt-nickel strikes used to plate on top of the lower chromium plate by ferrous articles falling off the plating racks and dissolving in the bath, and thus iron from this source as well as anodes and salts may plate out with the nickel, or cobalt, or cobalt-nickel alloy plate, and yet the 3 resulting plate is, for the purposes of this invention a nickel, cobalt or nickel-cobalt alloy plate. In fact, the iron content of all of the strike plates may be as high as to iron and still excellent results are obtained.

The importance of the lower underlying chromium plate in greatly improving the corrosion protection afforded by ductile bright nickel-cobalt alloy that is given a final bright chromium plate of 0.01 mil thickness can most quickly be seen by evaluation with the Corrodkote test or the acetic acid modified salt-spray test. For a description of these methods of corrosion testing, see W. L. Pinner, Accelerated Corrosion Tests for the Performance of Plated Coatings, Plating, vol. 44, page 763 (1957). Without the first underlying chromium layer of at least 0.01 mil and preferably of at least 0.03 mil thickness, Very bad corrosion failure is obtained for thicknesses of bright nickel-cobalt plate as high as about 1 mil.

However a very important factor not brought out very clearly by the accelerated tests was that, if cobalt plate or a cobalt-nickel plate of at least about 80% cobalt is present underneath the final or upper chromium plate then the latter tends to flake off after about 1 year outdoor exposure in an industrial atmosphere that is quite humid during late fall, winter, and early spring. The flaking off of the chromium is due to severe very shallow lateral corrosion attributable to the intense electrical couple between passive chromium and cobalt when exposed to an acidic industrial atmosphere. This harmful result occurring with the final outside chromium and cobalt is in fact a beneficial effect when cobalt or a relatively high cobaltnickel alloy overlies the underneath chromium and has a thickness under about 0.1 mil.

In general, the best results are obtained with a nickel strike or a cobalt-nickel strike on top of the underneath chromium layer followed by a bright nickel-cobalt plate containing about 40% cobalt, or the use of a ductile semibright nickel plate against the nickel strike or cobaltnickel strike followed by the bright nickel-cobalt alloy plate containing about 40% cobalt, the soft semi-bright nickel, preferably sulfur-free, constituting at least of the plate between the two chromium plates and the thicknesses of each layer being within the above given ranges.

After the first chromium plate, the plated articles are thoroughly rinsed, ultra-sonic vibration can be used to aid rinsing especially of blind holes which may entrap chromic acid or chromic salts, then dipped or soaked in 'a reducing solution to reduce hexavalent chromium to the less harmful trivalent chromium. Hydrogen peroxide solutions, sulfite solutions, dextrose, gluconic acid, tartaric acid or Warm oxalic acid solutions are satisfactory for the aqueous reducing solutions. The chromium plated articles are again rinsed thoroughly, then given a low pH nickel or nickel-cobalt or cobalt strike. These low pH nickel and cobalt-nickel and cobalt strike baths can tolerate appreciable concentrations of chromic acid, at least 1 gram/liter and trivalent chromium, at least 3 grams per liter, without the resulting plate having poor adhesion. However, it is nevertheless very important to keep the chromic acid in the low pH strike baths to minimum values in order to minimize dragging chromic acid into the main nickel or nickel-cobalt plating baths. in this connection it is advantageous in some cases to transfer from the first low pH strike to a second low pH strike to keep the chromic acid to a minimum in the subsequent transfer to the main nickel or nickel-cobalt plating bath. Hydrogen peroxide is a preferred reducing agent to use in the low pH strike baths to reduce chromic acid to trivalent chromium. Only sufficient peroxide should be used to just reduce the chromic acid since excess peroxide is undesirable. If suliite is used in the nickel strike to reduce chromic acid, no excess should be used as the sulfite ion is harmful in these low pH strike baths to both the covering power and in the quality of the plate. Oxalic acid may be used,"

but its action in reducing the hexavalent chromium is slow in the room temperature low pH strike baths.

Typically suitable nickel strike, cobalt strike, nickelcobalt alloy strike and nickel-cobalt alloy baths for use in forming the improved composite electroplates of this invention are given in the examples which follow, but it is to be understood that the baths and conditions given therein are illustrative only.

Example I Polished steel suitable for use as automobile hub caps is cleaned in a conventional manner and after a final alkaline anodic cleaner is rinsed, acid dipped or anodically etched, and then given a chromium plate of 0.03-0.06 mil thickness from the following hexavalent chromium bath:

CrO ozs./gal 40 (325 g./l.). SOL -ozs/gal 4 (3.25 g./l.). Temperature F. F. Cathode current density 300-500 amps/sq. ft. Plating time 5-10 minutes.

After the initial chrominum plating is finished, the hub caps are thoroughly rinsed, and given an agitated soak dip in a 5% solution of sodium sulfite, rinsed thoroughly in water and transferred to a low pH cobalt strike bath such as the following:

CoSO .7l-l O 75-150 grams/liter. CoCl .6H O 50-100 grams/liter. B 130 l5-30 grams/liter. Cone. HCl 5%10% by volume. Temperature Room.

Cathode current density 20-100 amps/sq. ft. Plating time 0.3-5 minutes.

This bath is purified electrolytically at a low current I density of, e.g., 2-10 amps. sq. ft. to eliminate zinc, copper and other harmful impurities, and is preferably also continuously or frequently treated with activated carbon. The cobalt salts may be fluoborate instead of chloride or sulfate or mixtures may be used.

After removal from the cobalt strike bath, the hub caps are then transferred to a ductile semi-bright type Watts nickel plating bath containing an addition agent selected from the class consisting, for example, bromal, chloral hydrate and coumarin, and plated with about 0.8 mil to about 1 mil of semi bright nickel, then transferred to a bright nickel plating bath containing a brightener selected from the class consisting of benzene sulfonamides and sulfonimides, preferably o-benzoyl sulfimide, together with an aliphatic unsaturated compound or compounds, and plated with about 0.2 to about 0.3 mil of bright nickel, then rinsed and transferred to a chromium bath of approximately the following compositions:

CrO ozs./gal 33.

SO ozs./gal 1.5-2.

Temperature 125 F.-l35 F. Cathode current density 285-325 amps./ sq. ft.

and plating on the bright nickel layer a thickness of bright chromium of 0.03-0.05 mil.

Example II Polished steel hub caps are put through the same steps given in Example I except that the cobalt strike bath was substituted for by the following nickel cobalt strike bath:

Cathode current density 20-100 amps/sq. ft. NiCl .6H O 50-100 grams/liter. NiS'O 6H O 50-100 grams/liter. H 50 15-30 grams/liter. Conc. HCl 5%-10% by volume. Temperature room.

Cathode current density 20-100 amps./ sq. ft.

Plating time l-l0 minutes.

. its use in Example II.

Example 111 Polished steel hub caps are put through the same steps given in Example I except that the cobalt strike bath was substituted for by the following nickel strike bath:

NiSO .6I-I O -200 grams/liter. NiCl .6H O 150-0 grams/liter. H BO 15-30 grams/liter. Conc.HCl %-10% by volume.

Temperature room.

Cathode current density 20-100 amps./sq. ft. Plating time about 1-10 minutes.

The bath is purified as described in Example I. The nickel salts may be fiuoborate instead of sulfate or chloride, or mixturm may be used.

After removal from the nickel strike the hub caps are then transferred to the following nickel-cobalt plating bath:

NiSO .6H O 100-200 grams/liter. CoSO .7H O 20-40 grams/liter. NiCl .6I-I O 30-200 grams/liter. H 130 30-45 grams/liter. Allyl sulfonate 0.3-2 grams/liter. o-Benzoyl sulfimide 1-3 grams/liter. Benzene sulfonamide l-3 grams/liter.

at 0.1-0.2 grams/liter, or

HO 3SCH2CE at 3-10 grams/liter. Air agitation preferred. Temperature at 130-l50 F., pH of 3.8-4.5.

CrO oz./gal 33. S0 oz./gal 1.5-2. Temperature 125 F.-135 F.

Cathode current density--amps./sq.ft. 285-325.

and plated to produce a bright chromium layer having a thickness of 0.03-0.05 mil.

Example IV Polished steel hub caps were put through the same steps given in Example III except that the nickel strike bath was substituted for by the nickel cobalt strike bath set forth above in Example II, and the conditions of forming the nickel cobalt strike in Example II were duplicated.

Example V Polished steel hub caps were given the initial chromium coating described in Example I, and the chromium was overlaid with a nickel cobalt strike layer by employing the nickel cobalt strike bath and conditions set forth for After removal of the hub caps from the nickel cobalt strike bath they were coated with a semi-bright nickel layer by using the bath described in Example I to produce a thickness of 0.5-1.2 mils. This semi-bright nickel layer was then overlaid with a nickel cobalt alloy plate having a thickness between 0.2 and 0.8 mil, by using the nickel cobalt bath set forth in Example III.

Example Vl Aluminum bumpers were cleaned and then anodized in a phosphoric acid solution and then given a low pH nickel strike, and then plated in a soft semi-bright nickel to a thickness of about 1 mil and then plated with the sequence in accordance with the procedure in Examples 2 and 4.

One of the unexpectedly important advantages of using cobalt containing strike baths and also cobalt containing nickel baths is that these baths will tolerate appreciably larger quantities of chromic acid without producing poorly adhered plate than straight nickel baths will tolerate.

What is claimed is:

1. A laminated corrosion protective final coating on a metal base susceptible to atmospheric corrosion comprising a first layer of chromium having a thickness in the range of about 0.01 to about 0.2 mil chromium, an adherent strike plate overlaying said chromium layer of a metal selected from the class consisting of cobalt, nickel and alloys thereof and having a thickness less than about 0.1 mil, said strike plate overlaid by plated metal selected from the class consisting of nickel and cobalt and alloys thereof containing at least 50% nickel, said plated metal being at least partially said nickel cobalt alloy when said strike plate is nickel, the sum of the thicknesses of said strike plate and said plated metal being in the range of about 0.2 mil to 2 mils, and a second chromium plate overlaying said plated metal and adherent thereto in a thickness of about 0.01 to about 0.1 mil.

2. A laminated coating in accordance with claim 1 wherein the said plated metal existing between the two said chromium plates comprises a bright nickel cobalt alloy plate containing from about 10% to 50% cobalt.

3. A laminated coating in accordance with claim 1 wherein the said plated metal between the two said chromium plates comprises a semi-bright nickel portion overlaid by a bright nickel-cobalt alloy containing from about 10% to 50% cobalt.

4. A laminated coating in accordance with claim 1 wherein said strike plate is nickel, and said plated metal comprises a ductile nickel portion overlaid by a bright nickel-cobalt alloy containing from about 10% to 50% cobalt.

5. A laminated coating in accordance with claim 1 wherein said strike plate is a nickel-cobalt, and said plated metal comprises a ductile nickel portion overlaid by a bright nickel-alloy containing about 10%-50% cobalt.

6. A laminated coating in accordance with claim 1 wherein said strike plate is a nickel-cobalt alloy and said plated metal is nickel.

7. A laminated coating in accordance with claim 1 wherein said plate is a nickel-cobalt alloy and said plated metal comprises a nickel-cobalt alloy containing from about 10% to 50% cobalt.

8. A laminated coating in accordance with claim 1 wherein said strike plate is a nickel-cobalt alloy and said plated metal comprises a semi-bright nickel portion overlaid by a bright nickel-cobalt alloy containing from about 10% to 50% cobalt.

9. A laminated coating in accordance with claim 1 wherein said strike plate is cobalt, and said plated metal is nickel.

10. A laminated coating in accordance with claim 1 wherein said strike plate is cobalt and said plated metal comprises a nickel-cobalt alloy containing from about 10% to 50% cobalt.

11. A laminated coating in accordance with claim 1 wherein said strike plate is cobalt and said plated metal comprises a ductile nickel portion overlaid by a bright nickel-cobalt alloy containing from about 10% to about 50% cobalt.

12. A laminated coating in accordance with claim 1 wherein said first chromium plate has a thickness in the range of about 0.03 to about 0.2 mil.

' 8 13. A laminated coating in accordance with claim 1 wherein the said first layer of chromium has a thickness in the range of about 0.03 to about .2 mil and is plated from a hexavalent chromium bath having a temperature in the range of 120 F.-180 F.

14. A laminated corrosion protective coating on a com mercial basis metal susceptible to atmospheric corrosion comprising a base layer of a semi-bright nickel plate having a thickness of 0.2 mil to 2.0 mils, said base layer being overlaid by a first layer of chromium having a thickness in the range of about 0.01 :to about 0.2 mil chromium, an adherent strike plate overlaying said chromium layer of a metal selected from the class consisting of cobalt, nickel and alloys thereof and having a thickness less than about 0.1 mil, said strike plate overlaid by plated metal selected from the class consisting of nickel and cobalt and alloys thereof containing at least 50% nickel, said plated metal being at least partially said nickel cobalt alloy when said strike plate is nickel, the sum of the thicknesses of said strike plate and said plated metal being in the range of about 0.2 mil to 2 mils, and a second chromium plate overlaying said plated metal and adherent thereto in a thickness of about 0.01 to about 0.1 mil.

15. A laminated corrosion protective coating on a commercial basis metal susceptible to atmospheric corrosion comprising a base layer selected from the class consisting of zinc and copper and alloys thereof having a thickness in the range of 0.1 to 2 mils, said base layer being overlaid by a first layer of chromium having a thickness in the range of about 0.01 to about 0.2 mil chromium, an adherent strike plate overlaying said chromium layer of a metal selected from the class consisting of cobalt, nickel and alloys thereof and having a thickness less than about 0.1 mil, said strike plate overlaid by plated metal selected from the class consisting of nickel and cobalt and alloys thereof containing at least 50% nickel, said plated metal being at least partially said nickel cobalt alloy When said strike plate is nickel, the sum of the thicknesses of said strike plate and said plated metal being in the range of about 0.2 mil to 2 mils, and a second chromium plate overlaying said plated metal and adherent thereto in a thickness of about 0.01 to about 0.1 mil.

16. A laminated corrosion protective coating on a commercial basis metal susceptible to atmospheric corrosion comprising an adherent zinc plate having a thickness in the range of about 0.01-1 mil on said basis metal surface, a copper plate overlaying said zinc plate and adherent thereto, having a thickness in the range of about 0.1 to about 0.5 mil, said copper plate being overlaid with a first layer of chromium having a thickness in the range of about 0.01 to about 0.2 mil chromium, an adherent strike plate overlaying said chromium layer of a metal selected from the class consisting of cobalt, nickel and alloys thereof and having a thickness less than about 0.1 mil, said strike plate overlaid by plated metal selected from the class consisting of nickel and cobalt and alloys thereof containing at least 50% nickel, said plated metal being at least partially said nickel cobalt alloy when said strike plate is nickel, the sum of the thicknesses of said strike plate and said plated metal being in the range of about 0.2 mil to 2 mils, and a second chromium plate overlaying said plated metal and adherent thereto in a thickness of about 0.01 to about 0.1 mil.

References Cited in the file of this patent UNITED STATES PATENTS 2,871,550 Weinberg Feb. 3, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,047,939 August 7, 1962 Henry Brown It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 41. after "he" insert used column 4 Example II Itine 67, for "Cathode current density" read CoSO .7H' O- Signed and sealed this 26th day of February 1963.

(SEAL) Attest:

ESTON G. Jonusou DAVID L. LADD Commissioner of Patents Attesting Officer 

1. A LAMINATED CORROSION PROTECTIVE FINAL COATING ON A METAL BASE SUSCEPTIBLE TO ATMOSPHERIC CORROSION COMPRISING A FIRST LAYER OF CHROMIUM HAVING A THICKNESS IN THE RANGE OF ABOUT 0.01 TO ABOUT 0.2 MIL CHROMIUM, AN ADHERENT STRIKE PLATE OVERLAYING SAID CHROMIUM LAYER OF A METAL SELECTED FROM THE CLASS CONSISTING OF COBALT, NICKEL AND ALLOYS THEREOF AND HAVING A THICKNESS LESS THAN ABOUT 0.1 MIL, SAID STRIKE PLATE OVERLAID BY PLATED METAL SELECTED FROM THE CLASS CONSISTING OF NICKEL AND COBALT AND ALLOYS THEREOF CONTAINING AT LEAST 50% NICKEL, SAID PLATED METAL BEING AT LEAST PARTIALLY SAID NICKEL COBALT ALLOY WHEN SAID STRIKE PLATE IS NICKEL, THE SUM OF THE THICKNESS OF SAID STRIKE PLATE AND SAID PLATED METAL BEING IN THE RANGE OF ABOUT 0.2 MIL TO 2 MILS, AND A SECOND CHROMIUM PLATE OVERLAYING SAID PLATED METAL AND ADHERENT THERETO IN A THICKNESS OF ABOUT 0.01 TO ABOUT 0.1 MIL. 